This invention is related to varactor television tuning systems which vary tuning frequency by a change in the application of voltage to a varactor diode tuning device. More specifically, it relates to the form of varactor television tuning systems which selectively tune to desired television channels according to a predetermined channel program sequence which has been stored in a memory.
A versatile memory tuning system is completely disclosed and claimed in application Ser. No. 466,597, filed May 3, 1974 in the names of John Ma & Akio Tanaka now U.S. Pat. No. 3,946,319 and entitled "All Electronic Digital Tuner System with Memory" and assigned to the assignee of the present application. The memory may be programmed in any desired sequence to provide sequential tuning among a selected group of channels. Storage locations are accessed at some convenient speed and tuning information is stored at individual locations. The advantages of such a tuning system with a memory are readily apparent since the viewer need sequence through only desired channels. The memory has sufficient capacity to hold the digits of the desired channel number, normally in binary encoded decimal form. The speed at which memory locations are accessed and the stored tuning information extracted is so rapid that the change of stored selections appears to be instantaneous.
A characteristic of all memory tuning systems is that they normally have two modes of operation, a program mode in which channel selections are mode and an operate mode in which channel selections are recalled. With varactor diode tuners, channel selection involves supplying a proper DC tuning voltage to the tuner. The mechanism for supplying the proper voltages may range from digitally accessed adjustable potentiometers to binary memories for storing channel numbers. In the operate mode the viewer then only sweeps through the limited number of preselected channel numbers for tuning to the desired channel.
Application Ser. No. 457,010, filed Apr. 1, 1974, in the name of John Ma and Akio Tanaka entitled "Digital Signal Seeking Tuning System" now U.S. Pat. No. 3,931,579 and assigned to the assignee of the present application discloses a television tuning system which includes channel counters operating sequentially to generate desired channel numbers. As each channel number is generated the system responds by tuning to the frequency location corresponding to the channel number. The system also utilizes signal recognition means to determine if a receivable signal is present at that frequency location and stops additional channel number generation until reactivated by the viewer. This use of channel counters to generate channel number information greatly simplifies the tuning system for the viewer, but no provision is made for a memory to store selected information.
A memory of the type which could store selected tuning information could be added to a channel counter system to provide for a convenient method of selecting from all possible channels only those channels which the viewer desires. Such a memory is described in the related application, Ser. No. 621,911. As with all memory systems, in the program mode the operator selects among all available channels and creates the sequence of desired channels available in his locations for subsequent viewing. In the operate mode the viewer chooses from those selected channels the particular channel he wishes to view.
With this system a single device, the counter, both generates the tuning information and accesses the memory location to determine if it has been selected. A problem arises in the operate mode; how to make the recall of stored selections so rapid that a change seems instantaneous yet permit a viewer time to react to which of the predetermined selections he wishes to view.
One form of multispeed selection system is known in the art. U.S. Pat. No. 3,914,698 to Leuschner shows an electronic "touch-tune" selector system using an up/down counter to activate utilization devices. The counter generates the addresses of various potentiometers so that a predetermined voltage can be supplied to various utilization means. In column 6, beginning at line 49, a multispeed feature of this system is described. In the normal operation of the preferred embodiment, any of 16 selector switches may be activated to cause corresponding utilization of one of 16 functions. When any switch is activated, the counter begins counting to generate the address of a corresponding voltage source and the addressed voltage source is activated. As an added feature, a remote control system is included. However, because of the limitation on the number frequencies available for control, no provision is made for the direct selection of the individual switches, rather only up and down commands are recognized. In the remote control mode, the speed of the counter is reduced so that an operator can observe the result and make his selection while moving through the 16 possible locations.
Although the Leuschner patent shows a two speed operation of a counter the speed is controlled by the source of the control signal. One speed for receiver touch-tune activation and the second speed for remote control. The present invention memory tuning system employs counters and includes apparatus for controlling the speed at which the counters advance to generate channel numbers which access the read/write memory. Although the counter sequentially advances through all channel numbers, the speed at which it does advance is controlled so that non-selected channel numbers advance at an extremely rapid speed. This speed is so fast, that the viewer is unable to perceive actual counting. By contrast, when channel numbers are generated which correspond to preselected channel numbers, the system slows counting and appears to pause so the viewer can perceive and make a decision about viewing a selected channel. This allows the viewer to rapidly search through any of his predetermined selected channels regardless of the number of channels selected. Thus, a viewer can make comfortable selection of any of his preselected channels.